Geochemistry and Tectonic Setting of Totmaj Tolcanic Rocks, SE of Kashan


Totmaj volcano-sedimentary rocks, located at south-eastern of Kashan, are mainly composed of basalt-andesite lava flow and pyroclastic rocks (various types of tuffs and agglomerate) which locally show an alternation with Oligocene fossiliferous shallow marine sedimentary rocks (limestone and sand-stone). Based on major and trace elements geochemical data, the Totmaj volcanic rocks are very similar to calc-alkaline lava. They contain high Al2O3 and low Mg# (100 Mg/(Mg+Fe2+). Their Zr/Y ratio is more than 3, typical of continental volcanic arc rocks. In terms of N-MORB normalized trace element patterns, they show enrichment in K and Pb relative to Nb, Rb, P, and Ti, and also have a wide range of Ta/Yb ratios (between 2.3 to 8.9) and limited values for Th/Yb (0.3 to 1.9), characteristic of subduction-related rocks from orogenic belts. Their enrichment of large ion lithophile elements (LILE) and light rare earth elements (LREE) demonstrate that they have been probably originated from partial melting of enriched mantle wedge when it has been encountered with the released fluids from a subducted oceanic crust.